Köll, Joonas

Abstract [en]

The morphology and elastic properties of foams are investigated using models accounting for the cellular structure. Different modeling approaches are evaluated and compared to the cellular structures of real foams. The aim is to find an approach that produces realistic models that can be adjusted to match morphology measures taken form real foams. The elastic properties are computed using finite element analysis and the results are compared with both experimental results from mechanical testing and existing analytical models. A generalization of the existing analytical models is suggested for better agreement with the modeling results.

In Paper A Voronoi and equilibrium foam models are generated and investigated. The Voronoi models are found to have a high content of short edges and small faces while conversion into equilibrium foams eliminates such small geometrical features. It is also seen that different seed point distribution algorithms generally result in different model topologies.

In Paper B the relations between the sphere packing fraction and the resulting degree of volumetric polydispersity are studied as well as the relations between polydispersity and a number of morphology parameters. Both Voronoi and equilibrium foams are investigated and compared with data from real foams. Such comparisons indicate that the used method is somewhat limited in terms of polydispersity but provides a controlled way of varying the foam morphology.

In Paper C equilibrium models are used to study the inuence of polydispersity, relative density and distribution of solid on the elastic properties of foams. It is found that the elastic moduli are very weakly coupled to the polydispersity while the inuence from the relative density and distribution of solid is considerably stronger. Existing analytical models from the literature are fitted to the results and generalizations are suggested for better agreement over the investigated range of relative density and distribution of solid.

In Paper D equilibrium foam models with prescribed polydispersity are generated, analyzed and compared to real foams. The polydispersity of real foams is measured in micro-CT images and the results are applied to the models. The elastic properties are computed and the results are compared with experimental results and previous models with significantly lower polydispersity. No clear relation is found between the elastic properties and the polydispersity of equilibrium foams.